The first man to pass close to Mars is driven insane by strange 'voices' he hears on his radio. He is unable to record the voices as the Van Allen radiation belts wipe the magnetic tapes clean, so doubt is cast on his account. United Nations Exploration Agency send their crack team to investigate. After landing on the planet's surface they find traces of an ancient civilisation, but then a disembodied Martian appears and demands its people be transported to Earth, where they will enslave the human race. One-by-one the crew are taken over.